U.S. Pat. No. 4,465,420, issued to this applicant, discloses a large capacity self-erecting portable silo assembly wherein the bin is transported on one trailer unit and a conveyor elevator for filling the bin has a wheeled truck under its charging end portion to comprise a second trailer unit. That patent points out the advantages of a self-erecting silo, which can be set up and taken down without the use of a crane.
The present invention relates to a portable self-erecting silo assembly of somewhat smaller capacity, having a bin and a conveyor elevator that can both be transported on a single trailer unit which also serves as a base frame for the erected silo.
U.S. Pat. No. 4,249,351 to J. D. Brock discloses such an assembly wherein the legs upon which the bin is supported in its erected position are pivotally connected to the bin and to the trailer unit bed, to swing between upright and horizontal positions. The legs remain parallel to one another as they swing down, so that the bin remains in an upright attitude in its transport position, and therefore it can have only a limited height--hence only a limited capacity--in order to be able to pass under bridges and overpasses when being transported along a highway.
The conveyor elevator in the assembly of the Brock patent is mounted on the same trailer bed that carries the bin. At the charging end of the elevator its frame has a pivot connection to the rear end of the trailer bed, to be swingable between a transport position in which the elevator is forwardly and upwardly inclined at a small angle to the horizontal and an operative position in which it has a steeper upward inclination. Links are connected between the elevator frame and the bin whereby the elvator is swung up to its operative position as the bin is raised to its erected position and is lowered with lowering of the bin. As the legs of the bin swing down towards their horizontal positions they are forwardly inclined, so that the bin is near the front of the trailer frame when it is in its transport position. However, the elevator is only a little shorter than the trailer frame, and therefore the side wall of the bin that faces the rear end of the trailer has a removable upper panel, to allow the upper end portion of the elevator to be received in the upper portion of the bin when the bin and the elevator are in their transport positions.
The portable silo of this prior patent was best suited for cooperation with a bin and elevator of relatively light construction. However, a satisfactory portable silo assembly, in addition to having an adequately large capacity, should be of sturdy construction and have a heavy-duty bin floor system, heavy-duty elevator chains and heavy bearings.
The bin of a silo assembly is substantially heavier than the elevator, and therefore provision for raising and controlledly lowering the bin presents a major problem. The assembly disclosed in the applicant's U.S. Pat. No. 4,465,420 comprises a hydraulic cylinder jack for raising the bin. As pointed out in that patent, a hydraulic cylinder jack mechanism is a practical expedient for lifting a heavy surge silo bin, but only if it is not required to have an unduly long extension and retraction stroke. This limitation to short-stroke jacks is in apparent conflict with the need for raising the bin to a substantial elevation, as demonstrated by the earlier U.S. Pat. No. 3,934,739, disclosing a self-erecting silo assembly requiring a multi-stage telescoping hydraulic cylinder which, when extended, was so long that it was likely to be bent by the lateral force components inevitably imposed upon it.
Employment of a winch for raising the bin presents a different but equally difficult problem. As can be seen from the above discussed Brock patent, the winch cable must be trained over the top of a sturdy mast or post in order to translate pull on the cable into a lifting force on the bin. The mast or post functions only when the silo is set up and taken down, and at all other times it tends to be a nuisance, taking up valuable space on the trailer bed and increasing the transport weight of the assembly.